U.S. patent application number 13/520013 was filed with the patent office on 2012-10-25 for material for spark plug electrode having excellent spark wear resistance and discharge properties.
Invention is credited to Muneki Nakamura, Kunihiro Tanaka.
Application Number | 20120269675 13/520013 |
Document ID | / |
Family ID | 44482940 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120269675 |
Kind Code |
A1 |
Tanaka; Kunihiro ; et
al. |
October 25, 2012 |
MATERIAL FOR SPARK PLUG ELECTRODE HAVING EXCELLENT SPARK WEAR
RESISTANCE AND DISCHARGE PROPERTIES
Abstract
A material for a plug electrode having not only excellent
oxidation wear resistance but also excellent spark wear, and also
having adequately-considered discharge properties in use is
provided. The present invention relates to a material for a plug
electrode, comprising 5% by mass or more and 30% by mass or less of
Cu, 0.1% by mass or more and 15% by mass or less of Ir, with the
balance being Pt. Alloying by combining two metals of Cu and Ir can
reduce discharge voltages and improve durability against spark
wear. With addition of only one of them, the effect of improving
spark wear properties is poor and the effect of reducing discharge
voltages cannot be expected.
Inventors: |
Tanaka; Kunihiro;
(Hiratsuka-shi, JP) ; Nakamura; Muneki;
(Hiratsuka-shi, JP) |
Family ID: |
44482940 |
Appl. No.: |
13/520013 |
Filed: |
February 16, 2011 |
PCT Filed: |
February 16, 2011 |
PCT NO: |
PCT/JP2011/053191 |
371 Date: |
June 29, 2012 |
Current U.S.
Class: |
420/466 |
Current CPC
Class: |
H01T 13/39 20130101;
C22C 5/04 20130101 |
Class at
Publication: |
420/466 |
International
Class: |
H01T 13/39 20060101
H01T013/39; C22C 5/04 20060101 C22C005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 2010 |
JP |
210-032189 |
Claims
1. A material for a plug electrode, comprising 5% by mass or more
and 30% by mass or less of Cu, 0.1% by mass or more and 15% by mass
or less of Ir, with the balance being Pt.
2. The material for a plug electrode according to claim 1 wherein
the content of Cu is 8% by mass or more.
3. The material for a plug electrode according to claim 1 wherein
the content of Cu is 10% by mass or more.
4. The material for a plug electrode according to claim 1 wherein
the content of Ir is 0.3% by mass or more.
5. The material for a plug electrode according to claim 1 wherein
the content of Ir is 8% by mass or more.
6. The material for a plug electrode according to claim 1 wherein
the content of Ir is 12% by mass or less.
7. The material for a plug electrode according to claim 1 wherein
the content of Ir is 4.5% by mass or less.
8. The material for a plug electrode according to claim 1 wherein
the content of Ir is 1% by mass or less.
9. The material for a plug electrode according to claim 1 wherein
the content of Ir is 0.3% by mass or less.
10.-20. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a material constituting a
center electrode and an earth electrode of a spark plug, which has
reliable durability particularly for spark wear and has excellent
discharge properties.
BACKGROUND ART
[0002] Spark plugs for combustion engines are required to have
excellent wear resistance to be durable over a long period of time
in harsh conditions in combustion chambers. To meet the required
properties, materials composed of Ir, Pt, Ni or an alloy thereof
have been used as a material constituting a center electrode and an
earth electrode which are main components of the plug (Patent
Document 1). These materials are known to be excellent for a plug
electrode as they have a high melting point and are less
susceptible to oxidation wear in high temperature and highly
oxidative combustion chambers.
Prior Art Document
Patent Document
Patent Document 1: Japanese Patent Application Laid-Open No.
2009-295427
[0003] In the development of materials for a plug electrode, focus
is often placed on the improvement of durability as described
above. Because they are used for an electrode (discharge
electrode), however, their discharge properties are also important.
In particular, although elevation in the inner temperatures and
precise electronic control have recently progressed in the field of
automobile engines and discharge properties may be used as an
important factor in selecting materials, there have been few
studies on this.
[0004] Furthermore, most of the conventional studies on the
durability of materials for a plug electrode have mainly discussed
the development of materials which have a high melting point and
are less susceptible to wear due to oxidation even in a highly
oxidative atmosphere as described above. However, plug electrodes
are worn by, in addition to oxidation wear, spark wear caused by
spark constantly formed during use. Therefore, although
conventional theories themselves are correct, it could be necessary
to consider the problem also from a standpoint of the resistance
against spark wear.
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0005] Under such circumstances, an object of the present invention
is to provide a material for a plug electrode having not only
excellent oxidation wear resistance but also excellent spark wear
properties, and also having adequately-considered discharge
properties in use.
Means for Solving the Problems
[0006] The present invention solves the above problem and provides
a material for a plug electrode, comprising 5% by mass or more and
30% by mass or less of Cu, 0.1% by mass or more and 15% by mass or
less of Ir, with the balance being Pt.
[0007] The material for a plug electrode according to the present
invention is a ternary alloy prepared by adding Cu (copper) to
platinum and further adding precious metal Ir (iridium) thereto.
Alloying by combining two metals of Cu and Ir in this way can
reduce discharge voltages and improve the durability against spark
wear. This means that the object of the present invention cannot be
achieved by adding either Cu or Ir only. More specifically,
addition of Cu only has little effect of improving spark wear
properties, while the effect of reducing discharge voltages cannot
be expected with an alloy prepared by adding Ir only (corresponding
to conventional art).
[0008] Also, in the present invention, the amounts of addition of
the respective alloy metals are limited. The present inventors have
found that when the amounts of addition of the metals fall outside
an appropriate range, not only spark wear properties and discharge
properties deteriorate, but also oxidation wear increases. In other
words, the amounts of addition of the respective alloy metals must
be controlled to maintain good balance of spark wear properties,
discharge properties and oxidation wear properties.
[0009] Hereinafter the constitution of the Pt alloy according to
the present invention will be described. Cu mainly has an action to
reduce the discharge voltage of alloy materials. The amount of
addition is determined to be 5 to 30% by mass because when the
amount is less than 5% by mass, discharge voltage is not easily
reduced, and when the amount is more than 30% by mass, wear is more
likely to occur due to high temperature oxidation. The content of
Cu is preferably 8% by mass or more and more preferably 10% by mass
or more. This is because discharge voltage is particularly
lowered.
[0010] The Pt alloy of the present invention contains 0.1% by mass
or more and 15% by mass or less of Ir in addition to Cu of the
above content. A small content of Ir further reduces the discharge
voltage and also reduces the wear amount of electrodes for spark
discharge. More specifically, the area of wear after spark
discharge is decreased to about 40% as compared to a Pt alloy
containing only Cu. In addition, unevenness in discharge voltages
is also decreased to improve voltage stability. The present
invention is characterized in that the resulting plug material has
high wear resistance and excellent discharge properties even if the
content of Ir is as low as described above.
[0011] The content of Ir is 0.1% by mass or more and 15% by mass or
less. When the content is less than 0.1% by mass, the effect of
inhibiting wear due to spark discharge is difficult to obtain, and
when the content is more than 15% by mass, it tends to be difficult
to process the resulting alloy. In the above content range, the
relatively higher the concentration of Ir, the higher the effect of
inhibiting wear due to spark discharge, and the relatively lower
the concentration of Ir, the better the high temperature oxidation
properties. Therefore, it is preferable to select a suitable Ir
content considering conditions of use of spark plugs depending on
which properties are important. More specifically, when importance
is attached to the effect of inhibiting spark wear, the content of
Ir is preferably 0.3% by mass or more, particularly preferably 8%
by mass or more. On the other hand, when importance is attached to
the high temperature oxidation properties, the content of Ir is
preferably 12% by mass or less, particularly preferably 4.5% by
mass or less, and more preferably 1% by mass or less. Furthermore,
when importance is attached to the balance of the two as described
above, the content of Ir is preferably 0.3 to 1% by mass.
[0012] The Pt alloy of the present invention described above is
produced by mixing constituent metals, melting and casting. The
resulting Pt alloy is processed into precious metal chips through a
method of forming the alloy into a sheet material or wire and then
cutting to a desired length to be used as a spark plug.
Advantageous Effect of Invention
[0013] The Pt alloy of the present invention is a plug material
having both high temperature oxidation wear resistance and spark
wear resistance. The Pt alloy of the present invention also has
improved stability with reduced unevenness in discharge
voltages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates the result of evaluation of wear
resistance and discharge properties corresponding to the Ir
content.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Hereinafter preferred Examples of the present invention will
be described. First, for the preliminary experiment, properties of
Pt--Cu alloy were evaluated to determine the influence of the
addition of Cu to Pt on discharge properties.
[0016] Small pieces (size: 2 to 10 mm) of Pt and alloy metal (Cu)
were prepared as raw materials and charged in a water-cooled copper
mold to provide a predetermined alloy composition. Then the
materials were melted through a high-frequency induction heating
method (levitation melting) in inactive gas and cast. The melting
conditions included an output of 40 kW and a frequency of 250 kHz,
and the whole alloy was melted to form a homogeneous composition.
After melting the alloy, the output was controlled to cool the
alloy gradually at a cooling rate of 200.degree. C./min, and the
remaining gas was discharged to produce void-free marble ingots (15
mm in diameter, 8 mm in thickness. Next the marble ingots produced
were put in a water-cooled copper mold so as to be in contact with
each other and the contact portions were irradiated with argon arc
to be melted and joined.
[0017] After integrating the marble ingots, the resultant was
hot-forged to form an ingot of 12 mm square. Subsequently, the
ingot was subjected to groove rolling, swaging and dice drawing to
form wire having a diameter of 0.6 mm. In these processing steps,
the ingot was heat-treated at 1000.degree. C. to 1200.degree. C. at
the stage where the reduction in area was 20% to 50%. Precious
metal chips having a length of 0.8 mm were cut from the wire. In
the above processing steps, no noticeable crack or disconnection
was observed in the materials processed. The metallographic
structure of the wire after processing was observed and as a result
the material was found to be homogeneous with uniform crystal
grains. The resulting precious metal chips were subjected to the
evaluation of the residual rate after high temperature oxidation
and discharge properties as follows.
[High Temperature Oxidation Wear Resistance]
[0018] The high temperature oxidation wear resistance of the
precious metal chips produced was evaluated. The chips were heated
in the air at 1200.degree. C. for 50 hours and the residual rate
was calculated based on the measurements of the weight before and
after the experiment.
[Discharge Properties]
[0019] A precious metal wire having .phi.0.6 mm was used to measure
the discharge voltage. The precious metal wire was used for a
center electrode and a grounding electrode and the gap between them
was set to be 1.0 mm. Current was discharged in nitrogen atmosphere
(6 atm) for 140 hours and the voltage was measured for about 2
minutes at intervals of 28 minutes. The maximum voltage and the
average voltage in each measuring interval were determined and the
maximum value of the maximum voltages, the average value of the
average voltages and the respective standard deviations were
calculated.
[Spark Wear Properties]
[0020] The wear amount for spark wear was also the subject of
evaluation. The spark wear was evaluated by measuring the area of
wear based on the dimensional measurements of the tip of the
precious metal chips before and after discharge property.
TABLE-US-00001 TABLE 1 Durability Alloy Residual rate Discharge
properties composition after high Maximum voltage Average voltage
(% by mass) temperature Spark wear Maximum Standard Average
Standard Pt Cu oxidation area voltage deviation voltage deviation
Reference Example 1 95.0 5.0 99.02% 6118 .mu.m.sup.2 12.81 kV 0.31
9.52 kV 0.19 Reference Example 2 90.0 10.0 98.31% 9149 .mu.m.sup.2
19.10 kV 0.78 8.34 kV 0.21 Reference Example 3 75.0 25.0 91.14%
2719 .mu.m.sup.2 15.00 kV 0.99 8.56 kV 0.20 Reference Example 4
55.0 45.0 61.33% 10095 .mu.m.sup.2 27.50 kV 0.43 8.56 kV 0.09
Comparative Example 1 100 -- 98.68% 7086 .mu.m.sup.2 13.44 kV 0.57
9.92 kV 0.19 * The maximum voltage means the maximum value of the
maximum voltages in each measuring interval. * The average voltage
means the average value of the average voltages in each measuring
interval.
[0021] Table 1 shows that when containing Cu, the Pt alloy is
effective in reducing the average voltage. On the other hand, an
increase in the Cu content is likely to cause a decrease in the
residual rate of Pt alloy after high temperature oxidation. For
this reason, and the balance between the reduction of discharge
voltage and wear due to high temperature oxidation is taken into
consideration, the content of Cu is set at 5 to 30% by mass in the
present invention.
[0022] Next, precious metal chips composed of Pt--Cu--Ir alloy were
prepared and subjected to the evaluation of the residual rate after
high temperature oxidation and discharge properties. The precious
metal chips were produced in the same manner as in the preliminary
experiment, and the residual rate after high temperature oxidation,
discharge properties and the spark wear amount after discharge were
similarly evaluated.
[0023] The result of evaluation is shown in Table 2. Table 2 shows
the result of evaluation of precious metal chips composed of Pt--Cu
alloy (Reference Example 2, alloy containing 10% of Cu) and those
composed of Pt--Ir alloy (containing 20% of Ir) for comparison.
Also FIG. 1 shows the result of evaluation of alloys in which the
concentration of Cu is constant (10% by mass) while the
concentration of Ir is changed.
TABLE-US-00002 TABLE 2 Durability Residual rate Discharge
properties Alloy composition after high Maximum voltage Average
voltage (% by mass) temperature Spark wear Maximum Standard Average
Standard Pt Cu Ir oxidation area voltage deviation voltage
deviation Example 1 Balance 10 0.5 97.15% 4884 .mu.m.sup.2 10.78 kV
0.43 7.45 kV 0.22 Example 2 Balance 10 0.9 96.54% 4116 .mu.m.sup.2
11.09 kV 0.32 8.47 kV 0.17 Example 3 Balance 10 10 91.98% 1539
.mu.m.sup.2 12.34 kV 0.55 8.07 kV 0.28 Example 4 Balance 10 15
91.12% 3166 .mu.m.sup.2 10.00 kV 0.20 8.37 kV 0.19 Example 5
Balance 17 8 91.99% 1640 .mu.m.sup.2 14.02 kV 0.41 8.44 kV 0.21
Example 6 Balance 23 2 92.02% 2602 .mu.m.sup.2 13.20 kV 0.36 8.51
kV 0.20 Reference Example 2 Balance 10 -- 98.31% 9149 .mu.m.sup.2
19.10 kV 0.78 8.34 kV 0.21 Comparative Example 1 100 -- -- 98.68%
7086 .mu.m.sup.2 13.44 kV 0.57 9.92 kV 0.19 Comparative Example 2
Balance -- 20 91.08% 8597 .mu.m.sup.2 18.72 kV 0.72 10.37 kV 0.08 *
The maximum voltage means the maximum value of the maximum voltages
in each measuring interval. * The average voltage means the average
value of the average voltages in each measuring interval.
[0024] Table 2 and FIG. 1 show that further addition of Ir to the
Pt--Cu alloy results in a significant decrease in the spark wear
area. It has also been found even for the discharge properties that
the effect of reducing the maximum voltage as well as the effect of
reducing the average voltage was produced, and also their
unevenness (standard deviation) was reduced. In this embodiment
alloys in which the total content of Cu and Ir was 25% by mass or
less were studied, and it has been shown that these alloys are
preferred as they can keep the residual rate after high temperature
oxidation at a high level.
[0025] Because processability is decreased when more than 15% by
mass of Ir is added, however, Ir is preferably added at 15% or
less. This has been proved from the result that when an alloy
prepared by adding more than 15% by mass of Ir was experimentally
formed into an ingot and then wire, disconnection frequently
occurred, and although processing was not completely impossible,
the production efficiency was low.
INDUSTRIAL APPLICABILITY
[0026] The present invention provides a material for a plug
electrode which has high wear resistance and is durable over a long
period of time. In addition, with little unevenness in discharge
voltages, the stability when using the plug is improved.
* * * * *